smp: Use nr_cpus= to set nr_cpu_ids early
Yinghai Lu [Wed, 10 Feb 2010 09:20:37 +0000 (01:20 -0800)]
On x86, before prefill_possible_map(), nr_cpu_ids will be NR_CPUS aka
CONFIG_NR_CPUS.

Add nr_cpus= to set nr_cpu_ids. so we can simulate cpus <=8 are installed on
normal config.

-v2: accordging to Christoph, acpi_numa_init should use nr_cpu_ids in stead of
     NR_CPUS.
-v3: add doc in kernel-parameters.txt according to Andrew.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1265793639-15071-34-git-send-email-yinghai@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Tony Luck <tony.luck@intel.com>

Documentation/kernel-parameters.txt
arch/ia64/kernel/acpi.c
arch/x86/kernel/smpboot.c
drivers/acpi/numa.c
init/main.c

index 736d456..51bceb0 100644 (file)
@@ -1772,6 +1772,12 @@ and is between 256 and 4096 characters. It is defined in the file
                        purges which is reported from either PAL_VM_SUMMARY or
                        SAL PALO.
 
+       nr_cpus=        [SMP] Maximum number of processors that an SMP kernel
+                       could support.  nr_cpus=n : n >= 1 limits the kernel to
+                       supporting 'n' processors. Later in runtime you can not
+                       use hotplug cpu feature to put more cpu back to online.
+                       just like you compile the kernel NR_CPUS=n
+
        nr_uarts=       [SERIAL] maximum number of UARTs to be registered.
 
        numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
index 40574ae..605a08b 100644 (file)
@@ -881,8 +881,8 @@ __init void prefill_possible_map(void)
 
        possible = available_cpus + additional_cpus;
 
-       if (possible > NR_CPUS)
-               possible = NR_CPUS;
+       if (possible > nr_cpu_ids)
+               possible = nr_cpu_ids;
 
        printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",
                possible, max((possible - available_cpus), 0));
index 678d0b8..eff2fe1 100644 (file)
@@ -1213,11 +1213,12 @@ __init void prefill_possible_map(void)
 
        total_cpus = max_t(int, possible, num_processors + disabled_cpus);
 
-       if (possible > CONFIG_NR_CPUS) {
+       /* nr_cpu_ids could be reduced via nr_cpus= */
+       if (possible > nr_cpu_ids) {
                printk(KERN_WARNING
                        "%d Processors exceeds NR_CPUS limit of %d\n",
-                       possible, CONFIG_NR_CPUS);
-               possible = CONFIG_NR_CPUS;
+                       possible, nr_cpu_ids);
+               possible = nr_cpu_ids;
        }
 
        printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",
index 7ad48df..b872546 100644 (file)
@@ -279,9 +279,9 @@ int __init acpi_numa_init(void)
        /* SRAT: Static Resource Affinity Table */
        if (!acpi_table_parse(ACPI_SIG_SRAT, acpi_parse_srat)) {
                acpi_table_parse_srat(ACPI_SRAT_TYPE_X2APIC_CPU_AFFINITY,
-                                     acpi_parse_x2apic_affinity, NR_CPUS);
+                                    acpi_parse_x2apic_affinity, nr_cpu_ids);
                acpi_table_parse_srat(ACPI_SRAT_TYPE_CPU_AFFINITY,
-                                     acpi_parse_processor_affinity, NR_CPUS);
+                                    acpi_parse_processor_affinity, nr_cpu_ids);
                ret = acpi_table_parse_srat(ACPI_SRAT_TYPE_MEMORY_AFFINITY,
                                            acpi_parse_memory_affinity,
                                            NR_NODE_MEMBLKS);
index 8451878..05b5283 100644 (file)
@@ -149,6 +149,20 @@ static int __init nosmp(char *str)
 
 early_param("nosmp", nosmp);
 
+/* this is hard limit */
+static int __init nrcpus(char *str)
+{
+       int nr_cpus;
+
+       get_option(&str, &nr_cpus);
+       if (nr_cpus > 0 && nr_cpus < nr_cpu_ids)
+               nr_cpu_ids = nr_cpus;
+
+       return 0;
+}
+
+early_param("nr_cpus", nrcpus);
+
 static int __init maxcpus(char *str)
 {
        get_option(&str, &setup_max_cpus);